I am working on wireless data transmission between three ESP32 modules (ESP32-WROOM-32D with PCB antenna) by ESP-NOW (a derivative of WIFI). They are within 0.5 meter apart and are blocked by some aluminum/plastic frames. There is no obvious EM interference nearby. Both modules are powered by USB with no peripheral attached. My code is almost identical to the Arduino tutorial (default 1M data rate, on WIFI channel 3, no encryption, compiled with ESP32-arduino 2.0.4).